I'm not asking if he was a white supremacist; clearly, he is.
But if we're going to analogize to Al Qaeda or ISIL, which seems to be the Hot New Idea, we've gotta be able to name the group.
What group was the El Paso killer part of? Is it distinguishable from other communities he was a part of?
But is it true that all 8chan users are devoted to white supremacy and mass killings? Doubtful.